Field
The present application relates to the improved control of solidification behavior during the melting and casting of metals where a clean melt and the limiting of loss of metal during the process are desired by the use of high power surface treatment.
Prior Art
Good casting or solidification processes are those in which the melt is clean during melting and casting. Presently, when castings are made the use of chills, insulation and exothermic compounds is common to affect temperature and thereby control solidification behavior. Clean melts and risers are often used for re-melts. Often, risers are heated so that the last solidification of the casting occurs at the riser top. In this application, solidification and solidification processes are used synonymously (see, for example, M. C. Fleming, Solidification Processing, McGraw-Hill, 1974).
Current methods for controlling solidification behavior include chills proposed in U.S. Pat. No. 7,017,648 by Newcomb et al. (2006), U.S. Pat. No. 6,840,062 by Dakan, Sr. et al. (2005), U.S. Pat. No. 6,298,898 by Mahadeva, et al. (2001), U.S. Pat. No. 5,027,881 by Horst, et al. (1991), U.S. Pat. No. 4,905,752 by Rama Prasad (1990) and U.S. Pat. No. 4,365,948 by Chaplain (1982). Also, the use of exothermic compounds to control solidification has been proposed in U.S. Pat. No. 6,446,698 by Soderstrom, et al (2002), U.S. Pat. No. 6,286,585 by Twardowska, et al (2001), U.S. Pat. No. 6,133,340 by Menon (2000), U.S. Pat. No. 5,263,534 by Ichikawa, et al. (1993), U.S. Pat. No. 4,694,884 by Butler, et al. (1987), U.S. Pat. No. 4,566,519 by Kawamura, et al. (1986) and U.S. Pat. No. 4,508,571 by Nakato, et al. (1985). Lastly, insulation in other forms employed to control solidification has been proposed by U.S. Pat. No. 7,134,478 by Ohtake, et al. (2006), U.S. Pat. No. 7,121,323 by Weyer, et al. (2006), U.S. Pat. No. 6,848,496 by Ban, et al. (2005), U.S. Pat. No. 5,884,687 by Schwarzkopf (1999), U.S. Pat. No. 5,622,218 by Pedroza-Conteras (1997) and U.S. Pat. No. 5,607,007 by Chandley (1997).
These current methods have limitations. Metal loss during oxidation is normally considerable during the manufacture of castings in air. These losses can often be the cause of impurities in re-melted alloys. Such metal loss due to oxidation is not adequately minimized by the employment of chills, insulation and exothermic compounds. Also, chemical treatments of exothermic compounds applied to surfaces may be toxic or otherwise environmentally harmful.
The use of chills and insulation may require specially designed molds and associated setting up that adds expense and time to the casting process. Often, the chills and insulation would need to be designed specifically for a specific application leading to a loss of flexibility and resulting increase in costs. Such devices may not be re-usable in many cases as well, adding again to the over-all cost of the process.
It is suggested by V. Rajamani, et al., in Enhancement of Heat Transfer Due to Plasma Flow in Material Processing Applications, American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD Volume 376 HTD, Issue 2, 2005, Pages 889-893 and in Heat-transfer enhancement using weakly ionized, atmospheric pressure plasma in metallurgical applications, Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science Volume 37, Issue 4, August 2006, Pages 565-570 that heat treatment employing low amounts of ions can result in cleaner aluminum and enhanced heat transfer. The present application shows that the exposure of a low-ion atmosphere to any surface, using the claimed device and method, results in cleaner surfaces and materials in general, not only aluminum, which at the time of the above articles was unanticipated.